The expression “communication terminal” is understood to mean any item of communication equipment, radio or wired, fixed or mobile (or portable) capable of connecting to a satellite network so as to exchange data in the form of signals with another item of equipment. It might therefore be, for example, a satellite communication terrestrial station, a satellite gateway, a fixed or mobile telephone, or an individual or collective reception terminal, or a fixed or portable computer or a personal digital assistant (or PDA) equipped with a satellite communication module.
As known by the person skilled in the art, certain satellite communication standards, such as for example DVB-RCS (for “Digital Video Broadcasting-Return Channel by Satellite”), have been designed for so-called star traffic that is to say traffic from communication terminals to satellite gateways, and vice versa. More precisely, the communications between a satellite gateway and communication terminals follow a so-called “outward” path, passing through a communication satellite, while the communications between communication terminals and a satellite gateway follow a so-called “return” path, passing through a communication satellite.
In the case, notably, of the DVB standard, the streams which follow the outward path are modulated according to the DVB-S2 standard (of TDM type), while the streams which follow the return path are modulated according to the DVB-RCS standard (of MF-TDMA type). Stated otherwise, a communication terminal sends in DVB-RCS and receives in DVB-S2, while a satellite gateway sends in DVB-S2 and receives in DVB-RCS.
In star traffic, traffic between two communication terminals coupled to one and the same satellite (“peer to peer” traffic) must pass through the satellite gateway, so doubling the transmission lag and mobilizing twice as many resources, which are valuable in the case of a satellite link.
To avoid doubling the transmission lag, a first solution consists for example in using a dedicated repeater satellite which serves only as transparent relay between the communication terminals. The traffic is then termed “mesh”. The traffic streams not being processed in the repeater satellite (so-called transparent mode), compatibility of the communication terminals with the DVB standard is then no longer ensured. Specifically, the communication terminals send and receive in DVB-RCS, so they must be equipped with a multicarrier demodulator and be suitable for TDMA synchronization. However, an MF-TDMA demodulator is relatively expensive. Furthermore, this solution is not compatible with what is called the interconnection of satellite coverages.
A second solution consists in demodulating in the communication satellite the mesh traffic originating from the return path so as to insert it into an outward path dedicated to said mesh traffic. In this case, the communication terminals must be equipped with two outward path demodulators if they want to utilize the traffic of mesh and star types simultaneously.
A third solution consists in demodulating in the communication satellite, on the one hand, the traffic (mesh) originating from the return path and intended for the outward path, and on the other hand, the traffic (star) originating from the outward path and intended for the return path, so as to insert the mesh traffic into the outward path. The communication terminals thus comply with the DVB standard, and TDMA synchronization is ensured by the communication satellite. This operating mode of the communication satellite is termed regenerative, as opposed to the transparent mode of the first solution. The drawback of this solution resides in the fact that the entirety of the star traffic (following the outward path) must form the subject of a demodulation, then of a processing and finally of a remodulation in the communication satellite, including when there is no mesh traffic to be inserted into the outward path, even though the proportion of mesh traffic is generally low, typically less than 30%, and moreover variable. For example, in the case of an application relating to Internet access, only the interactive applications and the links between different “spots” (or coverage zones) actually require a mesh communication (or “single hop”). The onboard regenerative processing processor is therefore greatly overdimensioned with respect to the actual requirements, this being penalizing with regard to consumption and therefore limits the capacities of the satellite and thus penalizes the cost-effectiveness of the installation.
No known solution affording complete satisfaction, the aim of the invention is therefore to improve the situation.